The present invention relates to a ring laser angular rate sensor, a so-called ring laser gyro. More particularly, it relates to a readout apparatus for such a ring laser gyro.
A so-called ring laser gyroscope is basically a laser apparatus having a ring type resonant cavity, typically triangular in configuration. The laser beam is directed around the triangular path by suitable mirrors positioned at each of the corners of the triangular structure. In most cases, there are two laser beams traveling in opposite directions relative to each other around the ring. The positioning of the mirrors in the corners of the ring, or triangle, direct the laser beams down the channels of the resonant cavity. At one of the corners, the mirror must take the form of a so-called beam splitter. There a portion of each of the laser beams is reflected into the resonating cavity while another portion of each of the beams is transmitted through the mirror into a readout assembly. Some examples of ring laser gyros are shown and described in U.S. Pat. Nos. 3,373,650; 3,390,606; 3,467,472; and 4,152,071, all of which are assigned to the assignee of the present application.
It is conventional in such readout arrangements that the mirror at the readout corner of the triangular path between the ring laser gyroscope body is formed on a flat substrate member having parallel inner and outer surfaces. A suitable prismatic readout member is then bonded to the outer surface of the substrate member. The prism is used to fold at least one of the laser beams to make both beams emerge from the prism in substantially the same direction. This produces an interference pattern which may then be detected as a function of the freqency difference of the two beams, hence of the rotation of the ring laser structure. In such structures, the alignment of the readout optics to combine the beams is generally time-consuming and expensive and frequently introduces stability problems.
In U.S. Pat. No. 4,288,163 there is shown a readout structure for ring-laser gyro wherein the readout prism also serves, in an incidental showing, as the substrate for a partially reflecting so-called beam-splitter. That structure, however, is a highly complex symetrical prism providing triple internal reflection of both beams to provide converging beams at the output thereof.